The elucidation of molecular alterations that occur during human breast cancer development may permit the identification of preventative strategies for women at high risk. Fifty seven proteins were identified whose expression levels varied between surgical biopsies containing matched normal ductal/lobular units and Ductal Carcinoma in Situ (DCIS) lesions using laser capture microdissection (LCM) and proteomics. Many of the proteins identified were previously unconnected with cancer, including proteins regulating the intracellular trafficking of membranes, vesicles, cancer prevention agents, proteins, ions and fatty acids. Other proteomic trends related to cytoskeletal architecture, chaperone function, apoptosis, genomic instability and the microenvironment. Molecular studies of altered Rab11a expression have been performed and are submitted for publication. Rab11 is involved in the intracellular trafficking of cell surface and receptor proteins. We hypothesized that Rab11 may alter the trafficking of physiologically relevant proteins in immortal human MCF-10A cells, with phenotypic consequences in tumor progression. MCF10A cells were transiently transfected with a control vector, wild type or a dominant-negative (DN) Rab11a, and examined for aspects of EGF receptor (EGFR) function. Expression of DN-Rab11a decreased EGFR recycling as measured by radioactive ligand:receptor complexes. Decreased EGFR recycling was associated with prolongation of Erk1/2 signaling, but had no effect on Akt signaling. Using phenotypic assays, expression of DN Rab11a inhibited tumor cell proliferation, but promoted cellular motility in Boyden chamber assays. The data are the first to identify coordinate recycling, signaling and phenotypic phenotypes associated with Rab11a expression. If confirmed to exert similar phenotypes in vivo, Rab11a may represent an interesting molecular target for prevention studies. Studies of CRABPII, another differentially expressed protein, are underway. MCF10A transfectants expressing low or high levels of CRABPII exhibited altered proliferative responses to retinoids. The mechanism of action is under investigation, and may help to improve the efficacy of retinoids as prevention agents.